The present invention relates to an engine brake system of a two-cycle engine, and more particularly to a system for increasing an engine braking effect of the two-cycle engine.
In order to increase the engine braking effect of a four-cycle diesel engine, a butterfly valve is provided in an exhaust passage. However, the butterfly valve having movable portions is not proper for using in the exhaust passage, because it is exposed to high temperature.
The two-cycle engine inherently has low pumping loss compared to the four-cycle engine, because the two-stroke cycle of the two-cycle engine completes four cycles with one revolution of a crankshaft. Consequently, a vehicle driven by the two-cycle engine has a small engine braking effect.
Japanese Patent Application Laid-Open 61-272425 discloses a two-stroke engine having a system for increasing the braking effect of the two-cycle engine. The two-cycle engine has a connecting passage for communicating a combustion chamber with an exhaust passage in parallel with the exhaust passage. The connecting passage has a rotary valve for communicating the combustion chamber with atmosphere through the exhaust passage. An opening area of the rotary valve changes in accordance with engine speed. When a throttle valve of the engine is further rotated from an idling position to a more closing position by turning a control grip on a steering bar of a motor cycle, the rotary valve is opened to communicate the combustion chamber with the atmosphere. Thus, gas in the chamber flows alternately passing through the valve in accordance with the reciprocation of a piston, generating resistance against the piston of the engine to increase the engine braking effect.
However, the engine braking effect is not sufficiently increased.